How to get a variable name as a string in PHP

From: http://mach13.com/how-to-get-a-variable-name-as-a-string-in-php


How to get a variable name as a string in PHP
PHP – Jean-Jacques Guegan
On rare occasions, you may need to retrieve a variable name as a string.

This handy little function retreives the name of the variable:

< ?php
      $my_var = 1;
      echo var_name ($my_var);
?>

will give ‘my_var’.

I started trying to find a solution to this problem, because I needed such a function and because questions about it appeared on several mailing lists and forums:
[PHP] Is there a way to get a variable name as a string?

most people said it was not possible…
Re: [PHP] Is there a way to get a variable name as a string?
From: Rasmus Lerdorf

In PHP it is possible to use a variable if you have its name as a string :

 
< ?php
    $iVarName = 'MaxSize';
    $$iVarName = 10;
    echo $MaxSize;
?>

But PHP does not natively include a way to get the name of a given variable.

This might be useful in situations where you design a function with a parameter passed by reference and you need to know which variable was sent as a parameter for this function.

The solution :
The following function retreives the variable name from a given variable:

< ?php
 function var_name (&$iVar, &$aDefinedVars)
    {
    foreach ($aDefinedVars as $k=>$v)
        $aDefinedVars_0[$k] = $v;
 
    $iVarSave = $iVar;
    $iVar     =!$iVar;
 
    $aDiffKeys = array_keys (array_diff_assoc ($aDefinedVars_0, $aDefinedVars));
    $iVar      = $iVarSave;
 
    return $aDiffKeys[0];
    }
 
?>

This function has to be called with a second parameter always set to the result of the function “get_defined_vars()”:

< ?php	
 var_name($iVar, get_defined_vars());
?>

How does it work ?
var_name compares the result of the function “get_defined_vars()” before and after modification of the variable whose name we want to find.
The initial set of defined variables passed as a parameter to var_name is first stored in “$aDefinedVars_0” and compared later.
Before modifying the value of the variable, its value is saved in $iVarSave.

$iVar

is then changed to something different :

$iVar=!$iVar;

$aDefinedVars keeps track of this modification and can be compare to $aDefinedVars_0 (its initial value). The difference is the variable we modified and we can get its name as a string in the key value of the array record.

The value of the variable is restored to its initial value kept in $iVarSave and the name of the variable is returned.
Example :
The following PHP code shows the function var_name in action:

< ?php
$v_1 = 1;                               echo 'var $',var_name ($v_1, get_defined_vars()),' = ',var_dump($v_1),'
'; $v_2 = 4; echo 'var $',var_name ($v_2, get_defined_vars()),' = ',var_dump($v_2),'
'; $v_3 = 'qwerty'; echo 'var $',var_name ($v_3, get_defined_vars()),' = ',var_dump($v_3),'
'; $v_4 = array('aa'=>'11','bb'=>'22',3); echo 'var $',var_name ($v_4, get_defined_vars()),' = ',var_dump($v_4),'
'; $v_5 = &$v_2; echo 'var $',var_name ($v_5, get_defined_vars()),' = ',var_dump($v_5),'
'; echo 'var $',implode (' / $',var_name ($v_5, get_defined_vars(),true)),' = ',var_dump($v_5),'
'; function test() { $v_1 = 'qwerty'; echo 'var $',var_name ($v_1, get_defined_vars()),' = ',var_dump($v_1),'

'; global $v_5; echo 'var $',var_name ($v_5, get_defined_vars()),' = ',var_dump($v_5),'

'; } test(); ?>

var_name can retreive the name of the variable in every case.

Application :
The most direct application of this function is, of course, a “dump” function.
Just call this “dump” function with the variable you want to monitor – do not forget to add the “get_defined_vars()” parameter…

< ?php	
 
function dump(&$v, &$aDefinedVars)
    {
    echo '
',implode (' / $',var_name ($v, $aDefinedVars, true)),' = ',print_r($v, true),'

'; } dump($v_4, get_defined_vars()); ?>

Going further :
The function var_name can be enhanced by adding the parameter $bShowAllRef to show, if set to true, all the references relating to the variable passed as a parameter:

 
< ?php
 
function var_name (&$iVar, &$aDefinedVars, $bShowAllRef=false )
    {
    foreach ($aDefinedVars as $k=>$v)
        $aDefinedVars_0[$k] = $v;
 
    $iVarSave = $iVar;
    $iVar     =!$iVar;
 
    $aDiffKeys = array_keys (array_diff_assoc ($aDefinedVars_0, $aDefinedVars));
    $iVar      = $iVarSave;
 
    return ($bShowAllRef? $aDiffKeys: $aDiffKeys[0]);
    }
 
?>

That’s it ! You can download the function here.

This code is free to use and published under the GPL license.

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